Carrying Amounts and Estimated Fair Values for Certain Financial Instruments (Parenthetical) (Detail) (Residential Mortgage Loans, USD $) In Millions, unless otherwise specified	Sep. 30, 2012	Dec. 31, 2011	Sep. 30, 2011
Residential Mortgage Loans
Fair Value, Balance Sheet Grouping, Financial Statement Captions [Line Items]
Loans measured at fair value on a recurring basis	$ 76	$ 65	$ 62

- Definition

This element represents the portion of the balance sheet assertion valued at fair value by the entity whether such amount is presented as a separate caption or as a parenthetical disclosure. Additionally, this element may be used in connection with the fair value disclosures required in the footnote disclosures to the financial statements. The element may be used in both the balance sheet and disclosure in the same submission. This item represents loan receivable as presented on the statement of financial position which may include mortgage loans held for investment, finance receivables held for investment, policy loans on insurance contracts, or any other loans which are due the Company as of the balance sheet date.

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